feat: Add Jujutsu diff handling to Helix

helix-term/Cargo.toml

@@ -13,10 +13,14 @@ repository.workspace = true
 homepage.workspace = true
 
 [features]
-default = ["git"]
+default = ["vcs"]
 unicode-lines = ["helix-core/unicode-lines", "helix-view/unicode-lines"]
 integration = ["helix-event/integration_test"]
+
+# All VCSes available for diffs in Helix
+vcs = ["git", "jujutsu"]
 git = ["helix-vcs/git"]
+jujutsu = ["helix-vcs/jujutsu"]
 
 [[bin]]
 name = "hx"

helix-vcs/Cargo.toml

@@ -24,9 +24,13 @@ imara-diff = "0.1.7"
 anyhow = "1"
 
 log = "0.4"
+# For `jujutsu`
+tempfile = { version = "3.10", optional = true }
 
 [features]
 git = ["gix"]
+jujutsu = ["tempfile"]
+
 
 [dev-dependencies]
 tempfile = "3.13"

helix-vcs/src/jujutsu.rs

@@ -0,0 +1,222 @@
+//! Jujutsu works with several backends and could add new ones in the future. Private builds of
+//! it could also have private backends. Those make it hard to use `jj-lib` since it won't have
+//! access to newer or private backends and fail to compute the diffs for them.
+//!
+//! Instead in case there *is* a diff to base ourselves on, we copy it to a tempfile or just use the
+//! current file if not.
+
+use std::path::Path;
+use std::process::Command;
+use std::sync::Arc;
+
+use anyhow::{Context, Ok, Result};
+use arc_swap::ArcSwap;
+
+use crate::FileChange;
+
+pub(super) fn get_diff_base(file: &Path) -> Result<Vec<u8>> {
+    let jj_root_dir = find_jj_root(file)?;
+
+    // We extracted the `jj_root_dir` from the file itself, if stripping the prefix fails
+    // something has gone very very wrong
+    let file_rel_to_dot_jj = file
+        .strip_prefix(jj_root_dir)
+        .expect("failed to strip diff path from jj root dir");
+
+    let tmpfile = tempfile::NamedTempFile::with_prefix("helix-jj-diff-")
+        .context("could not create tempfile to save jj diff base")?;
+    let tmppath = tmpfile.path();
+
+    let copy_bin = if cfg!(windows) { "copy.exe" } else { "cp" };
+
+    let status = Command::new("jj")
+        .arg("--repository")
+        .arg(jj_root_dir)
+        .args([
+            "--ignore-working-copy",
+            "diff",
+            "--revision",
+            "@",
+            "--config-toml",
+        ])
+        // Copy the temporary file provided by jujutsu to a temporary path of our own,
+        // because the `$left` directory is deleted when `jj` finishes executing.
+        .arg(format!(
+            "ui.diff.tool = ['{exe}', '$left/{base}', '{target}']",
+            exe = copy_bin,
+            base = file_rel_to_dot_jj.display(),
+            // Where to copy the jujutsu-provided file
+            target = tmppath.display(),
+        ))
+        // Restrict the diff to the current file
+        .arg(file)
+        .stdout(std::process::Stdio::null())
+        .stderr(std::process::Stdio::null())
+        .status()
+        .context("failed to execute jj diff command")?;
+
+    let use_jj_path = status.success() && std::fs::metadata(tmppath).map_or(false, |m| m.len() > 0);
+    // If the copy call inside `jj diff` succeeded, the tempfile is the one containing the base
+    // else it's just the original file (so no diff). We check for size since `jj` can return
+    // 0-sized files when there are no diffs to present for the file.
+    let diff_base_path = if use_jj_path { tmppath } else { file };
+
+    // If the command succeeded, it means we either copied the jujutsu base or the current file,
+    // so there should always be something to read and compare to.
+    std::fs::read(diff_base_path).context("could not read jj diff base from the target")
+}
+
+pub(super) fn get_current_head_name(file: &Path) -> Result<Arc<ArcSwap<Box<str>>>> {
+    let jj_root_dir = find_jj_root(file)?;
+
+    // See <https://github.com/martinvonz/jj/blob/main/docs/templates.md>
+    //
+    // This will produce the following:
+    //
+    // - If there are no branches:    `vyvqwlmsvnlkmqrvqktpuluvuknuxpmm`
+    // - If there is a single branch: `vyvqwlmsvnlkmqrvqktpuluvuknuxpmm (master)`
+    // - If there are 2+ branches:    `vyvqwlmsvnlkmqrvqktpuluvuknuxpmm (master, jj-diffs)`
+    //
+    // Always using the long id makes it easy to share it with others, which would not be the
+    // case for shorter ones: they could have a local change that renders it ambiguous.
+    let template = r#"separate(" ", change_id, surround("(", ")", branches.join(", ")))"#;
+
+    let out = Command::new("jj")
+        .arg("--repository")
+        .arg(jj_root_dir)
+        .args([
+            "--ignore-working-copy",
+            "log",
+            "--color",
+            "never",
+            "--revisions",
+            "@", // Only display the current revision
+            "--no-graph",
+            "--no-pager",
+            "--template",
+            template,
+        ])
+        .output()?;
+
+    if !out.status.success() {
+        anyhow::bail!("jj log command executed but failed");
+    }
+
+    let out = String::from_utf8(out.stdout)?;
+
+    let rev = out
+        .lines()
+        .next()
+        .context("should always find at least one line")?;
+
+    Ok(Arc::new(ArcSwap::from_pointee(rev.into())))
+}
+
+pub(super) fn for_each_changed_file(
+    cwd: &Path,
+    callback: impl Fn(Result<FileChange>) -> bool,
+) -> Result<()> {
+    let jj_root_dir = find_jj_root(cwd)?;
+
+    let out = Command::new("jj")
+        .arg("--repository")
+        .arg(jj_root_dir)
+        .args([
+            "--ignore-working-copy",
+            "log",
+            "--color",
+            "never",
+            "--revisions",
+            "@", // Only display the current revision
+            "--no-graph",
+            "--no-pager",
+            "--template",
+            "",
+            "--types",
+        ])
+        .arg(cwd)
+        .output()?;
+
+    if !out.status.success() {
+        anyhow::bail!("jj log command executed but failed");
+    }
+
+    let out = String::from_utf8(out.stdout)?;
+
+    for line in out.lines() {
+        let mut split = line.splitn(2, ' ');
+
+        let Some(status) = split.next() else { continue; };
+        let Some(path) = split.next() else { continue; };
+
+        let Some(change) = status_to_change(status, path) else { continue };
+
+        if !callback(Ok(change)) {
+            break;
+        }
+    }
+
+    Ok(())
+}
+
+/// Move up until we find the repository's root
+fn find_jj_root(file: &Path) -> Result<&Path> {
+    file.ancestors()
+        .find(|p| p.join(".jj").exists())
+        .context("no .jj dir found in parents")
+}
+
+/// Associate a status to a `FileChange`.
+fn status_to_change(status: &str, path: &str) -> Option<FileChange> {
+    // Syntax: <https://github.com/martinvonz/jj/blob/320f50e00fcbd0d3ce27feb1e14b8e36d76b658f/cli/src/diff_util.rs#L68>
+    Some(match status {
+        "FF" | "LL" | "CF" | "CL" | "FL" | "LF" => FileChange::Modified { path: path.into() },
+        "-F" | "-L" => FileChange::Untracked { path: path.into() },
+        "F-" | "L-" => FileChange::Deleted { path: path.into() },
+        "FC" | "LC" => FileChange::Conflict { path: path.into() },
+        // We ignore gitsubmodules here since they not interesting in the context of
+        // a file editor.
+        _ => return None,
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use std::path::PathBuf;
+
+    use super::*;
+
+    #[test]
+    fn test_status_to_change() {
+        let p = "helix-vcs/src/lib.rs";
+        let pb = PathBuf::from(p);
+
+        for s in ["FF", "LL", "CF", "CL", "FL", "LF"] {
+            assert_eq!(
+                status_to_change(s, p).unwrap(),
+                FileChange::Modified { path: pb.clone() }
+            );
+        }
+        for s in ["-F", "-L"] {
+            assert_eq!(
+                status_to_change(s, p).unwrap(),
+                FileChange::Untracked { path: pb.clone() }
+            );
+        }
+        for s in ["F-", "L-"] {
+            assert_eq!(
+                status_to_change(s, p).unwrap(),
+                FileChange::Deleted { path: pb.clone() }
+            );
+        }
+        for s in ["FC", "LC"] {
+            assert_eq!(
+                status_to_change(s, p).unwrap(),
+                FileChange::Conflict { path: pb.clone() }
+            );
+        }
+        for s in ["GG", "LG", "ARO", "", " ", "  "] {
+            assert_eq!(status_to_change(s, p), None);
+        }
+    }
+}

helix-vcs/src/lib.rs

@@ -8,6 +8,9 @@ use std::{
 #[cfg(feature = "git")]
 mod git;
 
+#[cfg(feature = "jujutsu")]
+mod jujutsu;
+
 mod diff;
 
 pub use diff::{DiffHandle, Hunk};
@@ -75,6 +78,8 @@ impl Default for DiffProviderRegistry {
         let providers = vec![
             #[cfg(feature = "git")]
             DiffProvider::Git,
+            #[cfg(feature = "jujutsu")]
+            DiffProvider::Jujutsu,
         ];
         DiffProviderRegistry { providers }
     }
@@ -88,6 +93,8 @@ impl Default for DiffProviderRegistry {
 pub enum DiffProvider {
     #[cfg(feature = "git")]
     Git,
+    #[cfg(feature = "jujutsu")]
+    Jujutsu,
     None,
 }
 
@@ -96,6 +103,8 @@ impl DiffProvider {
         match self {
             #[cfg(feature = "git")]
             Self::Git => git::get_diff_base(file),
+            #[cfg(feature = "jujutsu")]
+            Self::Jujutsu => jujutsu::get_diff_base(file),
             Self::None => bail!("No diff support compiled in"),
         }
     }
@@ -104,6 +113,8 @@ impl DiffProvider {
         match self {
             #[cfg(feature = "git")]
             Self::Git => git::get_current_head_name(file),
+            #[cfg(feature = "jujutsu")]
+            Self::Jujutsu => jujutsu::get_current_head_name(file),
             Self::None => bail!("No diff support compiled in"),
         }
     }
@@ -116,6 +127,8 @@ impl DiffProvider {
         match self {
             #[cfg(feature = "git")]
             Self::Git => git::for_each_changed_file(cwd, f),
+            #[cfg(feature = "jujutsu")]
+            Self::Jujutsu => jujutsu::for_each_changed_file(cwd, f),
             Self::None => bail!("No diff support compiled in"),
         }
     }

helix-vcs/src/status.rs

@@ -1,5 +1,6 @@
 use std::path::{Path, PathBuf};
 
+#[derive(Debug, PartialEq)]
 pub enum FileChange {
     Untracked {
         path: PathBuf,